EP0521741B1 - Liner for annular bending/temporing moulds - Google Patents

Description

The invention relates to bending / tempering techniques for glass sheets, and more particularly relates to the coating of the annular shapes involved in said techniques.

The so-called horizontal bending / tempering techniques generally involve a first bending phase, where the glass sheet previously heated in an oven above its softening temperature is applied for example by pneumatic means at least once against an element. upper consisting of a sheet metal or refractory ceramic plate. In certain cases, this element constitutes only a carrier means. In other cases, it constitutes a means of forming or pre-forming the glass sheet, it can then have a curve more or less close to that which it is desired to impart to the glass sheet.

But whatever its form and function, it will be designated later by the term of solid upper element.

Thus, the sheet can be sucked up as described in patent application EP-A-3 391 and / or lifted by a hot ascending gas stream against this form of bending as described in patent application FR-A- 2,567,508. It can also be lifted by mechanical means such as lugs or a lower shape which can have different configurations, as described in patent FR-B-2 009 278.

Then the glass sheet thus more or less preformed can then be deposited in a well-known manner also on a shape with a curved profile open at its center, more succinctly called annular mold, before being evacuated on said annular mold towards the tempering zone. thermal. This quenching consists in sending, from two boxes arranged below and above the glass sheet, jets of cooling gas approximately perpendicular to the two faces of said sheet.

This type of annular mold is commonly equipped with a coating specifically adapted to this type of quenching and to the constraints that it imposes. In fact, this coating must, in addition to withstanding temperatures between 650 and 800 ° C. and not marking the glass, be particularly permeable to air, so as not to impede the circulation of the cooling air under pressure from on either side of the glass sheet. Indeed, the air projected from the lower quenching box relative to the annular mold supporting the sheet must be able to also flow tangentially along the contact surface between the mold and the sheet, so that the periphery of the sheet is also properly tempered, which implies a mold coating which is sufficiently permeable to allow this flow.

Various coatings provided for these quenching frames are known in the art.

Usually, a mesh of refractory fibers with relatively wide meshes is proposed, of the order of at least one millimeter on a side, possibly, as recommended in US-A-4,906,271, by fixing the meshes with knots at the crossing points, so that homogenize the distribution of these crossing points, which constitute the main points of contact between mold coating and sheet.

Other types of process involve, to complete or replace the bending by application against a solid form then lowering onto a quenching mold, a real pressing of the sheet taken between the solid form above it and an annular mold of bending below it. Insofar as pressing involves considerable and fairly brutal mechanical forces imposed on the glass sheet at its periphery supported by the annular mold, the coating of said annular mold must have very specific characteristics and different from those required for coating a quenching mold.

Indeed, it must have a certain softness, so as to soften the contact with the glass sheet as much as possible and to erase any slight imperfections in the shape of the mold. It must also be relatively deformable and extensible, so that it can easily be fixed by stretching it over the mold, for example by pliers or hooks. It must be able to absorb the dust which could be at the mold / sheet interface, thus showing a certain porosity, so that this dust does not mark the surface of the softened glass.

It must also, of course, not itself mark the glass with its own surface texture. It must therefore be of a fairly dense and tight texture, a texture exhibited in particular by tight-knit metal knits indicated in patent application FR-A-2 644 156 and which makes it possible to obtain a contact surface with the sheet of glass as smooth and smooth as possible. Thus, during the relative sliding between the glass sheet and the annular mold, the risk of marks on the glass sheet, in particular in the form of claws, is avoided. During the actual pressing between the solid form and the annular mold, such risks are also avoided, guaranteeing a soft and smooth contact between glass and annular mold.

But this type of coating, precisely because of this dense texture, is therefore incompatible with use as a coating for tempering mold because, as we have seen previously, it would not allow effective tempering of the periphery of the glass sheet. by opposing the tangential flow of the cooling air.

In this case, it is then necessary to use for the quenching and for the pressing two annular molds having coatings of different natures.

But this implies an additional step of mold exchange, with all the problems of synchronization and increase in cycle time that this poses.

The authors of the present invention have sought to develop an annular mold whose contact surface with the glass sheet is capable of being suitable both for bending, in particular by pressing, and for thermal quenching in air.

One could consider carrying out the pressing operation of the glass sheet with the frame designed and coated for the thermal tempering operation, but this remains a compromise, which is not tolerable from the point of view of the optical quality of the glazing obtained only if the relative sliding glass / annular mold generator marks is very limited, that is to say in fact if the bending to be imparted to the glass sheet is quite modest.

A type of "bifunctional" annular mold capable of being suitable for relatively pronounced bending without marking the sheets is mentioned in patent EP-A-373 992. In this case, it is an annular mold comprising a fixed part relative to the mold support frame and a hinged wing relative to this fixed part, which, by folding during pressing against the upper solid form, makes it possible to obtain locally highly curved glass sheets. The fixed part is covered with a fairly wide mesh net for tempering, while the articulated wing is covered with a dense felt suitable for pressing. During the quenching, the same annular mold is used, but the wing is then in the unfolded position, so as not to interfere with the quenching at the level of the strongly curved edge of the leaf. This therefore means that this marginal area is left unsupported during quenching. this situation is likely to generate parasitic deformations subsequent to pressing, and it is necessary to take this into account, for example at the level of the curvature of the annular mold and / or the amplitude of said pressing by the articulated wing, in order to obtain the final product having the desired curvature.

By its very design, this mold can only be used if the desired strongly curved area is small and limited to one side of the glass sheet. Indeed, it is necessary that the glass sheet during tempering is supported by a fixed part large enough to prevent it from sagging, said fixed part being moreover not very curved and coated with a tempering fabric, the pressing being done essentially by the articulated wing. This mold is therefore not suitable for windows of complex shape, for example having curvatures in different directions near two of their opposite or adjacent edges.

It is also known from US-A-3,741,743 a coating for annular mold for bending and quenching, and comprising two types of superimposed fabrics, the first of thick texture reinforcing the second of finer texture which covers it and which is in contact with the periphery of the glass sheets.

By examining in detail how the bending of a glass sheet takes place by pressing, the authors of the invention have been able to observe the following phenomena, linked to the relative movement between the glass sheet and the annular mold during the pressing operation.

Before pressing begins, the glass sheet is flat, or possibly already partially curved during a prior preforming by applying the sheet against the full curved upper shape. But in either case, it is less curved than is the edge of the lower annular mold seen radially, said edge perfectly matching the curvature of the solid upper shape. The outline of the sheet therefore extends beyond the annular mold. The first contact between the sheet and the annular mold is thus made between the outer periphery of the mold and a part of the very localized glass sheet, which does not correspond to the outermost periphery thereof.

The sheet is then gradually pressed by relative approximation between the lower annular mold and the upper shape. The glass sheet therefore becomes more and more hollow. The surface of the glass sheet in contact with the annular mold on the one hand gradually widens, on the other hand moves towards the outermost periphery of the sheet. The contact surface of the annular mold with the sheet, for its part, widens symmetrically and moves towards the innermost periphery of the mold. Overall, there is thus a relative radial sliding of the periphery of the sheet relative to the width of the edge of the annular mold.

At the end of pressing, the sheet completely follows the radial curvature of the edge of the annular mold. It is then in contact on the one hand by its entire upper face with the solid form, and on the other hand by the outer periphery of its lower face with this time the inner periphery of the annular mold.

The authors of the invention then took advantage of these observations, in order to be able to propose an annular mold which could be suitable both for pressing and air tempering of glass sheets.

They have in fact realized that it is during the relative sliding which takes place during pressing that there is a great risk of marking the glass sheet, essentially while the glass sheet is in contact with the outer periphery of the mold. annular, and this is all the more true at the very start of the glass / mold contact, where the portion of the glass sheet which comes into contact with the mold has a very small surface area and must therefore withstand high localized mechanical pressures.

The authors then proposed to use the inner periphery of the annular mold as a support surface for the glass sheet during tempering, then only adapting the outer periphery thereof to the pressing operation, or more exactly to the relative sliding operation previously explained which is a prelude to the final pressing, or to any other bending operation, in particular by simple inertia, which induces this type of relative displacement glass / annular mold.

In the description of the following invention, the term "pressing" will also be used for convenience, to designate this first phase of relative sliding of the annular mold relative to the glass.

The invention therefore consists of a device for bending / tempering glass sheets brought to their softening temperature for bending and tempering, comprising upper bending means, in particular an upper solid element, and a lower annular mold. on which the glass sheets deform and relative to which the edge of said sheets moves due to the deformation, in particular by horizontal pressing between the upper bending means and the lower mold. This annular mold is designed so that the contact surface of its coating with the glass sheets at the start of their deformation on the mold, lying on the outer periphery of said mold, is adapted to the unmarked movement of the glass on said mold, and in such a way that, on the other hand, said contact surface at the end of the displacement, in particular at the end of pressing, lying on the inner periphery of said mold is suitable for tempering.

The invention also relates to the coating itself of this annular mold, with a contact surface with the glass sheets adapted as previously mentioned, that is to say having two juxtaposed surfaces, one intended to be located on the outer periphery of the mold and allowing unmarked sliding of the edges of the glass sheets on it, following the deformation of the glass sheets in particular by pressing, the other intended to be located on the periphery inside said mold and allowing thermal tempering in air of the curved glass sheets on the mold with interposition of the coating.

In this way, it advantageously eliminates most of the risks of marking, since the sheets meet an appropriate contact surface, that is to say very smooth and even, when they undergo the initiation of bending by sliding. In addition, a satisfactory tempering level is all the same obtained at the periphery of the sheet, since at the end of movement of the glass relative to the mold, in particular by pressing, until the end of the tempering operation, it finds itself in contact with a suitable surface, sufficiently breathable. There is therefore no longer any need for a single annular mold, in particular a mold usually used for quenching, since this usually has a significant edge width which can easily be distinguished. two aforementioned contact surfaces.

This allows obvious gains in speed, and therefore cost, for quality end products. This allows in particular, by using such an annular mold, to reduce the setting times. Indeed, any use of an annular mold requires tedious manual adjustments, first of all to ensure the concentricity of the contact surface with the glass of said mold with respect to the solid shape, and moreover to ensure the positioning of this contact surface in the horizontal plane, this is usually called adjusting the "attitude" of the mold. In the case of the invention, instead of using two annular molds, one for bending, in particular by pressing, the other for quenching, only one is used which fulfills these two functions, which has the consequence of dividing at least by two, which is far from being negligible, all the adjustment times relating thereto, and gaining simplicity.

The invention applies equally well to an annular mold comprising a continuous rail, as to an annular mold having a serpentine rail with for example at least one articulated part movable relative to the rest of the rail.

On this point, an essential advantage of the invention emerges: In fact, in a known manner, from a certain level of curvature to be imparted locally to a glass sheet, it is necessary to operate a pressing with a mold articulated annular. In this way, by rotation about an axis of the wing articulated with respect to the rest of the fixed mold, it is possible to bend the glass sheet in a pronounced manner avoiding this radial sliding movement of the mold / glass generating risks of marking. . But this articulation system is clearly much more complex in operation than that of a fixed mold, if only because there are additional relative movements to coordinate. However, from the moment when, according to the invention, an annular non-articulated mold is proposed so that the relative mold / glass movement does not cause any more marks thanks to a studied contact surface, then we can go back a lot more far the limit of the degree of curvature beyond which it is necessary to resort to a complex articulated annular mold.

In addition, beyond this new limit, by providing an articulated annular mold with the coating according to the invention, it is possible to carry out bending, possibly much more complex and / or pronounced than those usually obtained by an articulated mold, greatly reducing the risks of marking throughout said mold on the glass, in particular when the wing is relatively long compared to the rest of the mold.

It is further specified that if it is particularly advantageous to apply the invention to a mold intended for a real pressing operation between an upper mold and a lower annular mold, it can be applied a fortiori with the same success for annular molds intended in particular for bending under the simple effect of gravity.

In the case where, locally, during the first contact between the annular mold and the glass sheet, a part of the latter clearly protrudes from the mold, provision may be made to position a deflector at this point on the mold, extending the mold towards the exterior according to the curvature thereof. This deflector is then naturally provided with a smooth contact surface allowing the sliding of the glass, as in particular the surface previously mentioned under the term of surface suitable for pressing.

The contact surfaces of the annular mold are obtained by juxtaposition, in particular by sewing, of two types of coating, one suitable for the relative movement of the glass sheets relative to the annular mold, in particular by pressing, and the other for tempering. , the main thing being that the overall contact surface between the sheets and the annular mold has level continuity, in order to avoid any risk of marking the glass sheet when it slides from one of the coatings to the other. Similarly, one of the two coatings can completely or partially cover the other, as long as the level continuity is correctly ensured.

The subject of the invention is also a material, intended for coating for an annular mold serving as a support for the glass sheets during their bending and tempering, said material having at least two zones of distinct structures, in particular two different weaving or knitting structures, juxtaposed or partially overlapping, so as to that the contact surface with the glass sheets has a level continuity, with a dense zone having a smooth appearance for contact without roughness and another ventilated zone.

Preferably, this material is designed so that its dense part has an air permeability of between 1500 and 15000 and preferably between about 4000 and 10000, the other part with an aerated structure having a higher permeability. around 15,000. Permeability is defined in the context of the invention by the number of liters of air capable of passing through 10 cm ² of the material in question in one hour when they are projected onto the latter under a pressure of 100 Pa.

The material is in particular based on metallic refractory wires or fibers, for example in stainless steel or in a nickel-chromium alloy. It may also include non-metallic wires or fibers, in particular made of ceramic material such as silica.

It can be obtained advantageously by a modification of the knitting or weaving structure, that is to say by manufacturing in a single step the different parts of said material, one dense, the other airy, by modifying during knitting or weaving its texture and / or density.

It is specified that, preferably, the surface of said coating allowing the relative sliding of the glass sheets on the unmarked annular mold, in particular by pressing, is bonded to the mold.

Other details and advantageous features of the invention will appear during the detailed description below of nonlimiting exemplary embodiments.

According to the preferred embodiment of the invention, the coating consists of two parallel strips sewn to each other, the assembly being mechanically fixed, by clamps in particular, on the annular mold.

To give an order of magnitude of the relative widths of these two bands, we can give the following example: if we wish to cover an annular mold with an edge width of 60 mm, we can join a band adapted to the relative displacement glass / mold, especially for pressing with a width of 52 mm and a strip for quenching with a width of 8 mm.

These relative widths are in fact determined according to the annular mold considered and the manner in which the glass sheet rests on the mold during tempering. Indeed, whatever the radial width of the contact surface with the glass of the annular mold, it is preferable that the surface of the mold suitable for tempering corresponds as closely as possible to the glass surface supported by the mold. during the quenching operation. Advantageously, it is not chosen to be wider, since this would imply that part of the movement of sliding of the glass on the mold takes place on a surface suitable for tempering, which would entail increased risks of marking.

Insofar as any coating usually used for pressing, and more generally adapted to the relative movement of the glass sheets relative to the annular mold during bending, can thus according to the invention be combined with any coating usually used for tempering, first of all gives, without any limiting character, the characteristics of the coating part adapted to said relative movement without mark.

In all of the following tables, it is specified that the elongation is expressed as a percentage, and was measured in accordance with standard DIN 53857 at 20 ° C. on a sample of 200 x 50 mm drawn at a speed of 50 mm / min. The breaking load was measured according to the same standard and under the same conditions, but at different temperatures, its unit is in N / 5cm. The air permeability is measured in accordance with DIN ISO 4022 at 200 Pa and is expressed in l. dm ^-2 .mn ^-1 . The deformability at break is also expressed as a percentage.

A coating based on knitted metallic refractory fibers is used. Thus, the knitwear sold under the name Bekitherm KN / C1 / INC 601 and KN / C1 / 316L, Bekitherm KN / C2 / 316L and Bekitherm KN / C4 / 316L by the company Bekaert Fiber Technologies are adequate.

Their characteristics are as follows:
- Bekitherm KN / C1 / INC 601: nickel-chromium-based alloy Bekitherm KN / C1 / 316L: stainless steel alloy, which is interesting to use in the case where the annular mold is itself made of 316 alloy L, because this removes any risk of oxidation by a "pile" phenomenon between the metal of the mold and that of the fabric.
both have a knit thickness of 1 mm and a grammage of 700 g / m ² . 316 L INC 601 deformability at break direction of the rows of knitting 60 40 rib direction of knitting 90 90 breaking load knitting rows 300 (20 ° C) 220 (20 ° C) rib knitting 240 (20 ° C) 120 (20 ° C)
- Bekitherm KN / C2 / 316L is made of stainless steel. It has a thickness of 0.88 mm, a grammage of 650 g / m ² and a deformability at break in both directions greater than 50%.
- Bekitherm KN / C4 / 316L is made of nickel-chrome alloy. It has a thickness of 1 mm, a grammage of 875 g / m ² and a deformability similar to that of the Bekitherm KN / C2 / 316L.

Also advantageously used the coatings of the same company called Bekitherm NP 250-316L and Bekitherm NP 250 INC-601 based on the same alloys. It is a fabric structure surrounded on both sides by a felt layer called Bekinox based on stainless steel. In INC-601 or 316L, they have a similar grammage of 1500 g / m ² . Their physical characteristics are as follows: 316 L INC 601 breaking load minimum 1200 (20 ° C) minimum 1100 (20 ° C) minimum 1020 (350 ° C) minimum 825 (550 ° C) Elongation minimum 1 minimum 1 air permeability max 250 max 250

Likewise, any coating suitable for quenching can be used jointly. Thus, a mesh texture is advantageously used, from metallic refractory fibers, as patent FR-2 621 906 recommends. Preferably, stainless steel 316 L fibers are chosen. The preferred structure of the weaving consists of chains arranged parallel to one another, and linked transversely two by two by threads. Said chains are obtained from three threads, and each of the threads is obtained by association of tens of unitary fibers. Each mesh of the fabric thus obtained has a side of 2 to 8 mm, and preferably here less than 3 mm given the width of the strip that is taken.

According to another embodiment, the two bands are one, insofar as it is a knit whose mesh evolves so that it is tight at the level of the surface adapted to the pressing and wider at the surface suitable for quenching. We take either fibers based on 316 L stainless steel, or based on INC 601 which we combine in threads to be knitted. This advantageously makes the sewing operation between the two types of coating superfluous.

These embodiments are in no way limitative of the invention. We can thus combine any coating usually used specifically for quenching with any coating used specifically for bending involving a relative movement glass / mold, and in particular for bending by pressing, in the context of this invention.

The major advantage of the invention is that, without compromising on the quality of the bending, in particular by pressing and / or quenching, a single annular mold is used, the "mixed" coating of which is in some way perfectly suited to operations he must undergo by supporting the glass sheet.

These examples are therefore given only by way of illustration, and give the desired results, that is to say that no marking is observed on the curved / tempered glass sheets with molds thus coated, and the quenching level of the periphery of the sheets is satisfactory.

Claims (24)

1. Apparatus for bending/tempering glass sheets raised to their softening point with a view to their bending and tempering, comprising upper bending means, particularly a solid, upper member, and a lower annular mould provided with a covering and on which the bent sheets are thermally tempered in air, characterized in that the contact surface of the covering of said annular mould with the glass sheets at the start of the deformation thereof on the mould located on the outer periphery of said mould is adapted to the mark-free displacement on said mould, particularly being suitable for pressing and in that the contact surface of the covering of the annular mould with the glass sheets at the end of displacement, particularly at the end of pressing, is located on the inner periphery of said mould and is suitable for tempering.
2. Apparatus according to claim 1, characterized in that the annular mould has a continuous rail or a segmented rail having at least one part articulated with respect to the remainder of the rail.
3. Apparatus according to one of the claims 1 or 2, characterized in that the contact surfaces, one suitable for the relative displacement between the glass and the mould, particularly suitable for pressing, and the other for tempering the covering of the annular mould are obtained by at least two types of covering, which are either juxtaposed, or one of them totally or partly covers the other, so that the overall contact surface with the glass sheets of the annular mould has a level continuity.
4. Apparatus according to one of the claims 1 or 2, characterized in that the contact surfaces, one suitable for the relative displacement between the glass and the mould, particularly suitable for pressing, and the other for tempering the covering of the annular mould are obtained by a single covering, particularly a knitted fabric, whose mesh structure is dense at the contact surface suitable for the relative displacement between glass and mould and whose mesh structure is ventilated at the contact surface suitable for the tempering.
5. Apparatus according to claim 3, characterized in that in the case of a juxtaposing of the two covering types, this is brought about by sewing one to the other.
6. Apparatus according to any one of the claims 1 to 5, characterized in that the width of the contact surface suitable for tempering is approximately the same as that of the glass sheet supported by the annular mould during the tempering operation.
7. Apparatus according to any one of the claims 1 to 6, characterized in that the complete covering of the annular mould is held taut on said mould by mechanical means.
8. Apparatus according to any one of the claims 3 to 7, characterized in that each of the coverings is based on refractory metallic fibres, preferably of stainless steel or nickel/chrome alloy.
9. Apparatus according to any one of the claims 1 to 3 and 5 to 8, characterized in that the contact surface suitable for the relative displacement between the glass and the mould and in particular suitable for pressing, is obtained by a smooth covering, particularly in the form of a knitted fabric having dense meshes or a fabric associated with felt.
10. Apparatus according to any one of the claims 1 to 3 and 5 to 9, characterized in that the contact surface suitable for tempering is obtained by a very air-permeable covering, particularly in the form of a knitted fabric or gauze, both having wide meshes.
11. Apparatus according to any one of the claims 1 to 10, characterized in that the annular mould also has at least one deflector locally extending the same towards the outside following its curvature, the contact surface of said deflector with the glass sheets being suitable for the relative displacement between the glass and the mould, particularly during pressing, and in particular obtained by a smooth covering identical to that of the contact surface suitable for the relative displacement between the glass and the mould.
12. Material intended for the covering of moulds serving as a support for glass sheets during their bending and their tempering, characterized in that it has at least two zones of separate structures, which are juxtaposed or partly overlap, so that the total contact surface with the glass sheets has a level continuity with zones having a dense structure and a smooth appearance for a roughness-free contact and zones having a ventilated structure.
13. Material according to claim 12, characterized in that it is obtained by knitting and/or weaving.
14. Material according to claim 13, characterized in that it is based on metallic refractory fibres, preferably of stainless steel or a nickel-chromium alloy.
15. Material according to claim 13 or 14, characterized in that it has non-metallic threads or fibres, particularly made from a ceramic material such as silica.
16. Material according to one of the claims 13 to 15, characterized in that it is obtained by modifying the knitting or weaving structure.
17. Material according to one of the claims 12 to 16, characterized in that the zones having a dense structure have a permeability to air between approximately 1500 and 15,000 and preferably between approximately 4,000 and 10,000 and the zones having a ventilated structure have a permeability exceeding approximately 15,000.
18. Covering for an annular mould serving as a support for glass sheets during their bending and their tempering, characterized in that it has in contact with the glass sheets two juxtaposed surfaces, one intended to be placed on the outer periphery of said mould and allowing the mark-free sliding of the edges of the glass sheets thereon, following a deformation of the glass sheets, more particularly by pressing, whilst the other is intended to be located on the inner periphery of said mould and allows thermal tempering in air of the bent glass sheets placed on the mould with the interposing of said covering.
19. Covering according to claim 18, characterized in that whichever of the two surfaces allows the mark-free relative sliding thereon of the glass, particularly by pressing, is bonded to the mould.
20. Covering for an annular mould according to claim 18 or 19, characterized in that it is obtained by knitting and/or weaving.
21. Covering for an annular mould according to claim 20, characterized in that the juxtaposed surfaces are obtained by a modification of the knitting or weaving structure.
22. Covering for an annular mould according to any one of the claims 18 to 21, characterized in that it is based on refractory metallic fibres, preferably of stainless steel or nickel-chrome alloy.
23. Covering for an annular mould according to one of the claims 18 to 22, characterized in that it incorporates non-metallic filaments or fibres, particularly of a ceramic material such as silica.
24. Covering for an annular mould according to one of the claims 18 to 23, characterized in that the surface allowing the mark-free sliding is obtained by an area having a dense structure and permeability to air between approximately 1500 and 15000, preferably between approximately 4000 and 10000 and in that the surface allowing the thermal tempering in air is obtained by an area having a ventilated structure with a permeability to air exceeding approximately 15000.